Several aminosterol compounds have been isolated from the liver of the dogfish shark, Squalus acanthias. One of these compounds has been designated as 1436, the structure of which is shown in FIG. 1. Compound 1436 has been previously described in, e.g., U.S. Pat. Nos. 5,763,430; 5,795,885; 5,847,172; 5,840,936 and 6,143,738, each of which is incorporated by reference in its entirety, and has been shown to inhibit weight gain and suppress appetite, which leads to weight loss in animal models.
Diabetes is a major medical problem in the United States and increasingly so in the rest of the developed world. Type II diabetes in particular is caused primarily by the effects of a sedentary life style and a fat-rich diet. The diabetic individual is susceptible to medical problems directly related to his disease such as elevated serum cholesterol, high blood pressure, congenital obesity syndromes (including congenital leptin, pro-opiomelanocortin (POMC) and melanocortin-4 receptor (MC4R) deficiencies), and sleep apnea, especially in pickwickian syndrome. In addition, the accumulation of fat in the liver can progress to nonalcoholic steatohepatitis and cirrhosis. Another problem for obese diabetic individuals is an increased risk in any surgery that must cut through thick layers of fatty tissue that are highly vascularized and therefore prone to hemorrhage. Necessary surgery is frequently postponed until this diabetic patient can lose sufficient weight to make the risk of the operation acceptable.
Insulin is an important regulator of different metabolic processes and plays a key role in the control of blood glucose. Defects related to insulin synthesis and signaling lead to diabetes mellitus. Binding of insulin to the insulin receptor (IR) causes rapid autophosphorylation of several tyrosine residues in the intracellular part of the beta-subunit. Three closely positioned tyrosine residues (the tyrosine-1150 domain) must be phosphorylated to obtain maximum activity of the insulin receptor tyrosine kinase (IRTK), which transmits further signals via tyrosine phosphorylation of other cellular substrates, including insulin receptor substrate-1 (IRS-1) and insulin receptor substrate-2 (IRS-2).
Protein phosphorylation is a well-recognized cellular mechanism for transducing and regulating signals during different stages of cellular function (see, e.g., Hunter, Phil, Trans. R. Soc. Lund. B. 353: 583-605 (1998); Chan et al., Annu. Rev. Immunol. 12: 555-592 (1994); Zhang, Curr. Top. Cell. Reg. 35: 21-68 (1997); Matozaki and Kasuga, Cell. Signal. 8: 113-119 (1996)). There are at least two major recognized classes of phosphatases: (1) those that dephosphorylate proteins that contain a phosphate group(s) on a serine or threonine moiety (termed Ser/Thr phosphatases or dual specificity phosphatases or DSPs) and (2) those that remove a phosphate group(s) from the amino acid tyrosine (termed protein tyrosine phosphatases or PTPases or PTPs).
Several studies clearly indicate that the activity of the auto-phosphorylated IRTK can be reversed by dephosphorylation in vitro (reviewed in Goldstein, Receptor 3: 1-15 (1993)) with the tri-phosphorylated tyrosine-1150 domain being the most sensitive target for PTPases. This tri-phosphorylated tyrosine-1150 domain appears to function as a control switch of IRTK activity and the IRTK appears to be tightly regulated by PTP-mediated dephosphorylation in vivo (Faure et al., J. Biol. Chem. 267: 11215-11221 (1992)).
PTP1B has been identified as at least one of the major phosphatases involved in IRTK regulation through studies conducted both in vitro (Seely et al., Diabetes 45: 1379-1385 (1996)) and in vivo using PTP1B neutralizing antibodies (Ahmad et al., J. Biol. Chem. 270: 20503-20508 (1995)). Three independent studies have indicated that PTP1B knock-out mice have increased glucose tolerance, increased insulin sensitivity and decreased weight gain when on a high fat diet (Elchebly et al., Science 283: 1544-1548 (1999), Klaman et al., Mol. Cell. Biol. 20: 5479-5489 (2000), and Bence et al., Nature Med (2006)). Overexpression or altered activity of tyrosine phosphatase PTP1B can contribute to the progression of various disorders, including insulin resistance and diabetes (Ann. Rev. Biochem. 54: 897-930 (1985)). Furthermore, there is evidence which suggests that inhibition of protein tyrosine phosphatase PTP1B is therapeutically beneficial for the treatment of disorders such as type I and II diabetes, obesity, autoimmune disorders, acute and chronic inflammation, osteoporosis and various forms of cancer (Zhang Z Y et al., Expert Opin. Investig. Drugs 2: 223-33 (2003); Taylor S D et al., Expert Opin. Investig. Drugs 3:199-214 (2004); J. Natl. Cancer Inst. 86: 372-378 (1994); Mol. Cell. Biol. 14: 6674-6682 (1994); The EMBO J. 12: 1937-1946 (1993); J. Biol. Chem. 269: 30659-30667 (1994); and Biochemical Pharmacology 54: 703-711 (1997)). Agents that inhibit phosphatase activity and thereby inhibit dephosphorylation of the insulin signaling pathway, increase whole-body insulin sensitivity. This is therapeutically beneficial in treatment of insulin resistance associated with Type II diabetes and obesity.
In addition, it has been shown (Bence K K et al., Nat Med 8:917-24 (2006)) that neuronal PTP1B in the brain regulates body weight, adiposity and leptin action. Therefore, if a PTP1B inhibitor can cross the blood brain barrier it will not only sensitize the effect of insulin but also result in weight loss an added benefit in the treatment of type II diabetes and in addition the treatment of obesity and its complications.
There is also reported insulin resistance in Type I diabetes for which agents with PTP1B inhibitory activity would be a useful therapeutic. An insulin sensitizing agent in early type I diabetes or in a pre-diabetic statue might delay the onset of diabetes by increasing the sensitivity to insulin and thereby reducing the requirement for over-secretion of insulin from remaining insulin-producing beta-cells in the pancreas, i.e. sparing these cells from subsequent “burn-out” and death. It has also been shown (Jiang Z X and Zhang Z Y, Cancer Metastasis Rev. 2:263-72 (2008)) that inhibitors of PTP1B can prevent the growth of tumors and therefore be useful for the treatment of cancer.
The PTPase family of enzymes can be classified into two subgroups: (1) intracellular or nontransmembrane PTPases and (2) receptor-type or transmembrane PTPases. Most known intracellular type PTPases contain a single conserved catalytic phosphatase domain consisting of 220-240 amino acid residues. The regions outside the PTPase domains are believed to play important roles in localizing the intracellular PTPases subcellularly (Mauro, L. J. and Dixon J. E., TIBS 19: 151-155 (1994)). The first of the intracellular PTPases to be purified and characterized was PTP1B (Tonks et al., J. Biol. Chem. 263: 6722-6730 (1988)). Other examples of intracellular PTPases include (1) T-cell PTPase (TCPTP) (Cool et al., Proc. Natl. Acad. Sci. USA 86: 5257-5261 (1989)), (2) neuronal phosphatases STEP (Lombroso et al., Proc. Natl. Acad. Sci. USA 88: 7242-7246 (1991)), (3) PTP1C/SH-PTP1/SHP-1 (Plutzky et al., Proc. Natl. Acad. Sci. USA 89: 1123-1127 (1992)), (4) PTP1D/Syp/SH-PPT2/SHP-2 (Vogel et al., Science 259: 1611-1614 (1993); Feng et al., Science 259: 1607-1611 (1993)).
Receptor-type PTPases consist of (a) a putative ligand-binding extracellular domain, (b) a transmembrane segment, and (c) an intracellular catalytic region. The structure and sizes of the putative ligand-binding extracellular domains of receptor-type PTPases are quite divergent. In contrast, the intracellular catalytic regions of receptor-type PTPases are very homologous to each other and to the intracellular PTPases. Most receptor-type PIPases have two tandemly duplicated catalytic PTPase domains. The first PTPase receptor subtypes identified were (1) CD45 (Ralph, S. J., EMBO J. 6: 1251-1257 (1987)) and (2) LAR (Streuli et al., J. Exp. Med. 168:1523-1530 (1988)). Since then, many more receptor subtypes have been isolated and characterized, including, e.g., PTPalpha, PTPbeta, PTPdelta, PTPepsilon and PTPxi. (Krueger et al. EMBO J. 9: 3241-3252 (1990)).
Although agents have been identified for use as PTP1B inhibitors, such as the heteroaryl- and aryl-amino acetic acids described in WO 01/19831, WO 01/19830, and WO 01/17516, these agents do not exhibit separation of the inhibitory activity between PTP1B and TCPTP. Furthermore, because of the potential immunosuppressive effects resulting from inhibiting TCPTP, selective inhibition of PTP1B over TCPTP would make such agents more suitable for drug development as they could diminish or eliminate undesired side effects resulting from such nonselectivity.
Therefore, there is a need for a drug that can safely treat diabetes by the selective inhibition of PTP1B. In addition, if neuronal PTP1B is inhibited rapid weight loss can be induced in obese individuals thus also treating the effects of obesity, prevent neurodegeneration or Alzheimer's. A drug of this type would also be useful for the treatment of complications due to obesity, obesity in type II diabetes, high serum cholesterol, sleep apnea (especially in pickwickian syndrome), nonalcoholic steatohepatitis and surgery for obese patients. Finally, a PTP1B inhibitor could also be useful for the treatment of cancer.